This invention relates generally to a method for encoding polymers by incorporation of low levels of monomer residues distinct from the bulk monomer residues.
U.S. Pat. No. 4,431,766 discloses a method for coding a polymeric material by adding a trace amount of a compound detectable by instrumental methods. However, this reference suggests only addition of materials to a pre-formed polymeric material; a potential disadvantage of this method is that the added material could be removed from the polymeric material. Moreover, many of the heavy metals suggested by the ""766 patent would be objectionable on the basis of toxicity. There is no suggestion in the ""766 patent that the added material should be incorporated into the polymeric material itself.
The problem addressed by this invention is to find a method for encoding information into a polymer for later retrieval for purposes of identification.
The present invention is directed to a method for encoding a polymer. The method comprises incorporating, into a polymer formed by polymerizing at least one bulk monomer, from 0.1 ppm to 1% each of at least two additional monomer residues.